1. Technical Field
The present invention relates to a column end joint structure for joining a wooden column to a joining member (member to be joined) such as a wooden beam and a foundation in a wooden building, and more particularly to a column end joint structure in which transmission of a bending moment is facilitated between the column and the joining member.
2. Related Art
In a wooden building, it is proposed to adopt a Rahmen structure (rigid-frame structure) as a structural framework in which a joining between a wooden column and a wooden beam or that between a wooden column and a foundation is implemented by a so-called rigid coupling which is capable of transmitting a bending moment. With such a structure, when forces in a horizontal direction act on the structure repeatedly in a reciprocating manner such as during an earthquake, the bending moment and shearing force are generated at a joint portion between the column and the beam or at a joint portion between the column and the foundation. Further, the structural framework will have high quake resistance if these joint portions are equipped with sufficient strength against the bending moment and the shearing force generated at the time of an earthquake.
A joint structure for a Rahmen structure that employs wooden columns is disclosed, for example, in Patent Literature 1.
In this joint structure, at two positions on an end of a wooden column, the column is joined to a beam or a foundation via respective joint fittings, and the joint structure is configured as described below.
The column has a flat shape wherein a length of one side of a rectangular cross-section thereof is larger than a length of an adjacent another side. At an end of this column, a rectangular cutout is provided in each of both ends in a longitudinal direction of an end face. A screw member is threaded into the column in an axial direction thereof from inside the cutout. A bolt hole extending the axial direction from the end face is formed in this screw member. The joint fitting is arranged inside the above-mentioned cutout portion provided in the column, and is attached to the column by a bolt which is threaded into the bolt hole from the end face of the screw member. Further, this joint fitting is coupled to the foundation or the beam that is to be joined to the column by the bolt.
In such a joint structure, the column resists the bending moment with tensile force which is transmitted from the column via the screw member, the bolt, and the joint fitting to the foundation or the beam and with compression force which is transmitted from the column via the joint fitting to the foundation or the beam. Further, the bolt which is threaded into the screw member and couples the joint fitting and the column, and the bolt which couples the joint fitting and the foundation or the beam mainly resists shearing force.
[Patent Literature 1] JP-A-2013-204228
However, with such a joint structure as described above, the following problem may occur when a high bending moment and high shearing force act on it.
At the joint portion between the column and the foundation or that between the column and the beam, splitting stress acts in the column when the high bending moment and the high shearing force act on the joint portion. In other words, the force that causes generation of a crack along the axial direction of the column acts on the wooden column at the portion where the screw member is threaded into the column. While the screw member and the bolt for coupling the joint fitting are effective for resisting the bending moment when being threaded into the column at a position in the vicinity of the both ends in the longitudinal direction of the cross-section of the column, splitting tends to be generated more easily when the screw member and the bolt are threaded into the column at a position in the vicinity of the both ends in the longitudinal direction of the cross section of the column. When the splitting is generated at the position where the screw member has been threaded into the column, there arises a possibility of degradation of resistance of the joint portion against the bending moment and the shearing force.
Such a problem occurs not only in a case where the screw member is threaded into the wooden column and then the bolt is threaded from the end face thereof to fix the joint fitting, but also occurs in a similar manner in a case where the joint fitting is fixed to the column via a bolt, a rod-shape member, or the like inserted in the vicinity of an end edge.
The present invention has been made in view of above circumstances, and it is therefore, a purpose of the present invention is to provide a column end joint structure that can control generation of the splitting at an end of a column made of wooden material and that can control expansion of a splitting width even when the splitting is generated.